1. Field of the Disclosure
The present disclosure relates to digital radio broadcast transmission and reception of media content for synchronized rendering at a digital radio broadcast receiver.
2. Background Information
Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers. One type of digital radio broadcasting, referred to as in-band on-channel (IBOC) digital audio broadcasting (DAB), uses terrestrial transmitters in the existing Medium Frequency (MF) and Very High Frequency (VHF) radio bands. HD Radio™ Technology, developed by iBiquity Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception.
IBOC digital radio broadcasting signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated carriers or in an all-digital format wherein the analog modulated carrier is not used. Using the hybrid mode, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog-to-digital radio while maintaining their current frequency allocations.
One feature of digital transmission systems is the inherent ability to simultaneously transmit both digitized audio and data. Thus the technology also allows for wireless data services from AM and FM radio stations. The broadcast signals can include metadata, such as the artist, song title, or station call letters. Special messages about events, traffic, and weather can also be included. For example, traffic information, weather forecasts, news, and sports scores can all be scrolled across a radio receiver's display while the user listens to a radio station.
IBOC digital radio broadcasting technology can provide digital quality audio, superior to existing analog broadcasting formats. Because each IBOC digital radio broadcasting signal is transmitted within the spectral mask of an existing AM or FM channel allocation, it requires no new spectral allocations. IBOC digital radio broadcasting promotes economy of spectrum while enabling broadcasters to supply digital quality audio to the present base of listeners.
Multicasting, the ability to deliver several audio programs or services over one channel in the AM or FM spectrum, enables stations to broadcast multiple services and supplemental programs on any of the sub-channels of the main frequency. For example, multiple data services can include alternative music formats, local traffic, weather, news, and sports. The supplemental services and programs can be accessed in the same manner as the traditional station frequency using tuning or seeking functions. For example, if the analog modulated signal is centered at 94.1 MHz, the same broadcast in IBOC can include supplemental services 94.1-2, and 94.1-3. Highly specialized supplemental programming can be delivered to tightly targeted audiences, creating more opportunities for advertisers to integrate their brand with program content. As used herein, multicasting includes the transmission of one or more programs in a single digital radio broadcasting channel or on a single digital radio broadcasting signal. Multicast content can include a main program service (MPS), supplemental program services (SPS), program service data (PSD), and/or other broadcast data.
The National Radio Systems Committee, a standard-setting organization sponsored by the National Association of Broadcasters and the Consumer Electronics Association, adopted an IBOC standard, designated NRSC-5, in September 2005. NRSC-5 and its updates, the disclosure of which are incorporated herein by reference, set forth the requirements for broadcasting digital audio and ancillary data over AM and FM broadcast channels. The standard and its reference documents contain detailed explanations of the RF/transmission subsystem and the transport and service multiplex subsystems. Copies of the standard can be obtained from the NRSC at http://www.nrscstandards.org/SG.asp. iBiquity's HD Radio technology is an implementation of the NRSC-5 IBOC standard. Further information regarding HD Radio technology can be found at www.hdradio.com and www.ibiquity.com.
Other types of digital radio broadcasting systems include satellite systems such as Satellite Digital Audio Radio Service (SDARS, e.g., XM Radio, Sirius), Digital Audio Radio Service (DARS, e.g., WorldSpace), and terrestrial systems such as Digital Radio Mondiale (DRM), Eureka 147 (branded as DAB Digital Audio Broadcasting), DAB Version 2, and FMeXtra. As used herein, the phrase “digital radio broadcasting” encompasses digital audio broadcasting including in-band on-channel broadcasting, as well as other digital terrestrial broadcasting and satellite broadcasting.
As described above, one advantage of digital radio broadcasting systems is that they provide the capability to transmit multiple services, including audio and data, over one AM or FM frequency. For certain applications, such as displaying album art, image slide shows, scrolling text information, closed captioning, and product purchase information, it may be desirable to synchronize the content contained in one service with content contained in another service or to synchronize subservices or components of the same service.
Conventional techniques known to the inventors for transmitting content for synchronized rendering by a receiver place responsibility and processing requirements for synchronization on the receiver. For example, the MPEG Transport System, which can be used to transmit synchronized video content and audio content to be synchronized, includes a Program Clock Reference (PCR) 27 MHz clock signal in the Transport Stream for synchronization of the video and audio. Each video packet and audio packet separately includes a Decode and Presentation Time Stamp referenced to the PCR that permit the receiver to determine when the packet should be decoded and rendered. As another example, Synchronized Media Integration Language v. 3.0 (SMIL) requires the receiver to know the state of rendering primary content (e.g., how long an audio track has been playing) and provides attributes that may specify a begin time to render secondary content (e.g., album art) based on the rendering of primary content, thus permitting the receiver to decode that information to provide proper synchronization. As another example, SMIL also provides attributes that may specify a begin time to render secondary content at a predetermined universal coordinated time (UTC) regardless of the state of rendering the primary content.
However, the present inventors have found that none of these techniques is entirely satisfactory for synchronizing content in the currently deployed HD Radio broadcast system. This system includes multiple and varying signal processing paths on the transmit and, optionally, the receive side that should be accounted for when synchronizing services or subservices. In addition, digital radio broadcast receivers typically include a baseband processor that decodes the audio content and the data content and outputs audio to speakers. The data is then directed to a host controller that processes and renders the data as media content. However, the host controller typically has no knowledge of the audio samples, including the state of playback, since the audio is sent directly from the baseband processor to the speakers. The present inventors have determined that conventional synchronization approaches are not helpful for such receiver configurations and use of conventional approaches would require undesirable modifications at the receiver side.